Add support for MEI export and import of MuseScore IDs

[lpugin]

Adds an option so enable the use of MuseScore EIDs in the MEI export.

The option is not selected by default at this stage.

When selected, MEI elements take the MuseScore EID as @xml:id whenever appropriate, always prefixed with mscore-

<note xml:id="mscore-1786706395156" dur="8" pname="b" oct="4">

The LastEID is stored in the mei@xml:id, also prefixed with mscore-. The values are preserved in the importer. When re-exporting the file, only the mei@xml:id is expected to change in the same way is does with MuseScore files.

[rettinghaus]

Great, thank you.

Still two problems with the current approach:

• If someones manipulates the IDs, MuseScore will crash on trying to read the file
• If you copy and paste passages, you get duplicated xml:ids

Try this file to see duplicated IDs:

DotsPlacement.zip

Also there needs to be an additional check on assigning them on load if they are valid.

[lpugin]

If someones manipulates the IDs, MuseScore will crash on trying to read the file

Yes, this needs to be documented and users should be explained MuseScore IDs should not been edited or made up. I am planning to add that in the documentation.

If you copy and paste passages, you get duplicated xml:ids

Yes, this should be fixed, but it can be done separately since this is not strictly related to the MEI exporter.

[rettinghaus]

@cbjeukendrup Anything in the way for this to be merged?

[cbjeukendrup]

Sorry, I had lost track of it. I'll look into it again tonight. At this point, it would be good to rebase it, since there have been some changes to MuseScore's id system recently.

(Update: it looks fine in principle, but really needs a rebase to fix conflicts not detected by Git, since #25666.)

[rettinghaus]

@lpugin could you please do a rebase and adjust this to the changes in EID?

[lpugin]

There is now one issue with string EID containing /, which is not allowed in MEI xml:ids. Any ideas?

[cbjeukendrup]

VTest failure is unrelated; a rebase would fix it, but it's fine